Limits of magnetic interactions in Ni-Nb ferromagnet-superconductor bilayers*

Studies of ferromagnet-superconductor hybrid systems have uncovered magnetic interactions between the competing electronic orderings [1]. The Electromagnetic Proximity Effect predicts the formation of a spontaneous vector potential inside a superconductor placed in proximity to a ferromagnet [2]. In this work, we use a Nb superconducting layer and Ni ferromagnetic layer to test for such magnetic interactions. We use the complementary, but independent, techniques of polarised neutron reflectometry and detection Josephson junctions to probe the magnetic response inside the superconducting layer at close to zero applied field. In this condition, Meissner screening is negligible, so our measurements examine only additional magnetic and screening contributions from proximity effects. We report that any signals attributable to such proximity effects are below the detection resolution of our experimental study. From our measurements, we estimate an upper limit of the size of the zero field Electromagnetic Proximity Effect in our Ni-Nb samples to be ±0.27 mT [3].

 

[1] Flokstra M G, et al. Nat. Phys. 12 57–61 (2016)

[2] Mironov S, et al. Appl. Phys. Lett. 113 022601 (2018)

[3] Satchell N, et al. arXiv:2209.15366 (2022)